Embodiments of the invention relate to inkjet printing systems and methods. More specifically, the invention pertains to inkjet printing systems and methods that incorporate dot-matrix fonts to form images on a print medium. In addition, embodiments of the invention also relate to thermal inkjet printing systems that utilize the dot matrix font.
Dot matrix font or formatting is a fundamental component for inkjet printing systems. Inkjet printheads include an array of orifices (also referred to as “nozzles”) on the printhead wherein each nozzle is associated with an ink ejection chamber. Ink is ejected from the nozzles and chambers in droplet form onto a print medium in response to print commands generated by a controller. In thermal inkjet printing systems resistive heaters at the ejection chambers heat the ink in the chamber causing the ink to vaporize forming rapidly expanding pressure bubbles that force the ink drops from the chamber. The piezo-type printheads use mechanically vibrating piezo-transducers to eject the ink drops from the chambers and nozzles. In either type, the printhead may be mounted on a carriage that moves the printhead back and forth on an X-axis relative to a print medium, which is moving in a Y-axis direction relative to the printhead. In other inkjet printing systems, the printhead may remain stationary relative to movement of the print medium.
Images or characters are formed on the print medium by ejecting the ink drops according to an arrangement of dots in a dot matrix consisting of rows and columns of pixels. Each pixel represents a potential ink drop or dot. The arrangement of the dots relative to one another on the dot matrix dictates which nozzles eject ink to form an image, and the timing of the ejections. The quality of an image printed depends in part on the resolution capabilities of the printing system. Resolution is measured as the number of ink drops that can be printed in one linear inch. A typical desk top inkjet printer has resolution capabilities of three hundred dots per inch (300 dpi). In order to increase resolution, the dot size (consequently nozzle size) may be decreased. In addition, the ejection frequency for a nozzle (number of times a nozzle is fired for a given time interval) may be increased to fit more dots within a determined space. This allows for optimal dot overlap to minimize white spaces and jagged edges in a printed character.
With respect to single-pass printing, for example in production line printing, two factors constrain printable dot density. The maximum vertical dot density is limited by the physical spacing of the nozzles as arranged on the printhead. In addition, the maximum horizontal dot density is limited by the maximum frequency (drops/second) at which a nozzle can eject drops divided by the relative speed of the printhead or print medium. Higher speeds mean lower horizontal drops per inch.
A typical printhead nozzle arrangement includes at least two columns (first column and second column). The nozzles in each column are horizontally offset relative to one another; and, the first and second columns are vertically offset relative to one another. Print command signals are multiplexed such that, the columns eject ink simultaneously, and ink drops generated from the second column fill in gaps or spaces in an ink dot column generated by the first nozzle column. In addition, the rate at which the printhead and/or print medium move relative to one another and the frequency at which the nozzles are capable of firing determine a horizontal dot density. These factors provide a maximum dot overlap with a relatively high resolution, if the print medium or printhead are moving at a given rate of speed. However, if the rate of speed of the printhead or print medium is increased or too high relative to the printhead/nozzle maximum ink ejection frequency, the dot overlap and resolution is compromised.